In 3GPP (Third Generation Partnership Project), in a radio communication system corresponding to LTE (Long term Evolution), for which the standards are being set up currently, a radio base station eNB assigns a radio resource in the radio communication between the radio base station eNB and a radio terminal UE (for example, see Non Patent Literature 1). Furthermore, in a radio communication system corresponding to LTE, either Frequency Division Duplex (FDD) or Time Division Duplex (TDD) is employed in the radio communication between the radio base station eNB and the radio terminal UE.
Moreover, in an LTE (TDD-LTE) radio communication system employing the TDD, there has been discussed a feature where a radio base station eNB performs control for adaptively directing a beam (adaptive array control) toward the radio terminal UE at the time of transmission of a downlink radio signal, in order to ensure communication quality between the radio base station eNB and a radio terminal UE that is moving.
According to a technique of calculating the antenna weight, when a radio base station eNB receives a sounding reference signal (SRS), which is an uplink radio signal from a radio terminal UE, it is considered that the radio base station eNB calculates an antenna weight for a downlink resource block that has a frequency band equal to a frequency band of the SRS.
However, in a TDD-LTE radio communication system, the frequency band that the radio terminal UE can use once for transmitting SRS can be used in the radio communication between the radio base station eNB and the radio terminal UE, in other words, the frequency band is narrower than the entire frequency band of the downlink resource block that can be assigned to the radio terminal UE, and is also fixed. Therefore, even though some of the downlink resource blocks can be assigned, SRS having a frequency band equal to the frequency band of the downlink resource blocks does not exist because of which an antenna weight might not be set.